Problem: $ { {-3} \times \left[\begin{array}{rr}{1} & {4} \\ {0} & {4}\end{array}\right] = {?} } $
To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{-3}\times{1} & {-3}\times{4} \\ {-3}\times{0} & {-3}\times{4}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-3} & {-12} \\ {0} & {-12}\end{array}\right]}$